Knudsen Number

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

Knudsen number, abbreviated Kn, is a dimensionless number that is used in fluid dynamics to determine what type of analysis should be used to model an object moving through a fluid. It is defined as the ratio of the molecular mean free path length to a representative physical length scale. This calculation determines the Knudsen number, the length or the lambda value based on your inputs.

Knudsen Number Formula

$$\large{ Kn = \frac{ \lambda }{ l } }$$

Where:

$$\large{ Kn }$$ = Knudsen number

$$\large{ l }$$ = length

$$\large{ \lambda }$$ (Greek symbol lambda) = mean free path

Solve for:

$$\large{ l = \frac{ \lambda }{ Kn } }$$

$$\large{ \lambda = Knl }$$